如何在Base64中正确编码和解码字符串？

Question

I want to encode a string in Base64 for later decoding it. I encode it doing this:

public static String encryptString(String string) {     
    byte[] bytesEncoded = Base64.getEncoder().encode(string.getBytes());
    return (new String(bytesEncoded));
}

Then, the encoded string is stored on disk using UTF-8. After restarting the application, the encoded string is readed from disk and I'm trying to decode the string using this:

public static String decryptString(String string) {
    byte[] valueDecoded = Base64.getDecoder().decode(string);
    return (new String(valueDecoded));
}

Something is wrong because it is giving me this exception:

java.lang.IllegalArgumentException: Illegal base64 character d
at java.base/java.util.Base64$Decoder.decode0(Base64.java:743)
at java.base/java.util.Base64$Decoder.decode(Base64.java:535)
at java.base/java.util.Base64$Decoder.decode(Base64.java:558)

This is a TRACE step by step

1º i encode this: {"configuration":{"shop":{"name":"","addressLine1":"","addressLine2":"","postalCode":"","city":"","country":"","phoneNumber":""}},"jointBets":[],"groups":[{"name":"Test","members":[]}]}

into this: eyJjb25maWd1cmF0aW9uIjp7InNob3AiOnsibmFtZSI6IiIsImFkZHJlc3NMaW5lMSI6IiIsImFkZHJlc3NMaW5lMiI6IiIsInBvc3RhbENvZGUiOiIiLCJjaXR5IjoiIiwiY291bnRyeSI6IiIsInBob25lTnVtYmVyIjoiIn19LCJqb2ludEJldHMiOltdLCJncm91cHMiOlt7Im5hbWUiOiJUZXN0IiwibWVtYmVycyI6W119XX0=

2º i store it on disk in utf8

3º i retreive it from disk and it's this string:

eyJjb25maWd1cmF0aW9uIjp7InNob3AiOnsibmFtZSI6IiIsImFkZHJlc3NMaW5lMSI6IiIsImFkZHJlc3NMaW5lMiI6IiIsInBvc3RhbENvZGUiOiIiLCJjaXR5IjoiIiwiY291bnRyeSI6IiIsInBob25lTnVtYmVyIjoiIn19LCJqb2ludEJldHMiOltdLCJncm91cHMiOlt7Im5hbWUiOiJUZXN0IiwibWVtYmVycyI6W119XX0=

4º i decode it and get the exception.

Answer 1

My guess is that you are not specifying a charset. Try running the below maybe with and without the charset specified for the String constructor to verify.

   @Test
    public void base64Test() throws Exception{
        String string = "ABCDF";

        byte[] bytesEncoded = Base64.getEncoder().encode(string.getBytes());
        String encodedStr = (new String(bytesEncoded,Charset.forName("ISO-8859-1")));
        System.out.println(encodedStr);

        byte[] valueDecoded = Base64.getDecoder().decode(encodedStr);
        String decodedStr = (new String(valueDecoded,Charset.forName("ISO-8859-1")));
        System.out.println(decodedStr);
    }

Answer 2

Then, the encoded string is stored on disk using UTF-8. After restarting the application, the encoded string is readed from disk and I'm trying to decode the string using this:

This seems to be a point of failure. Most likely your problem is OS/JDK dependent Apparently the following code seems to work well for me (Win 7, latest JDK 1.8):

public static void main(String[] args) throws IOException {
    String source = "{\"configuration\":{\"shop\":{\"name\":\"España\",\"addressLine1\":\"\",\"addressLine2\":\"\"," +
                "\"postalCode\":\"\",\"city\":\"\",\"country\":\"\",\"phoneNumber\":\"\"}},\"jointBets\":[]," +
                "\"groups\":[{\"name\":\"Test\",\"members\":[]}]}";

    // Encode string
    String encoded = encryptString(source);

    System.out.println("Base64 encoded: " + encoded);

    // Temp Dir
    String tempDir = System.getProperty("java.io.tmpdir");

    // Write to File
    try (BufferedWriter writer = new BufferedWriter(new FileWriter(tempDir + "data.txt"))) {
        writer.write(encoded);
    }

    // Read from File
    Path path = Paths.get(tempDir + "data.txt");

    Stream<String> lines = Files.lines(path);
    String dataFromFile = lines.collect(Collectors.joining("\n"));
    lines.close();

    // Compare content
    assert encoded.equals(dataFromFile);

    // Decode string
    String decoded = decryptString(dataFromFile);
    System.out.println("Base64 decoded: " + decoded);
}

public static String encryptString(String string) {
    byte[] bytesEncoded = Base64.getEncoder().encode(string.getBytes(StandardCharsets.UTF_8));
    return new String(bytesEncoded);
}

public static String decryptString(String string) {
    byte[] valueDecoded = Base64.getDecoder().decode(string);
    return new String(valueDecoded);
}

Base64 encoded: eyJjb25maWd1cmF0aW9uIjp7InNob3AiOnsibmFtZSI6IkVzcGHDsWEiLCJhZGRyZXNzTGluZTEiOiIiLCJhZGRyZXNzTGluZTIiOiIiLCJwb3N0YWxDb2RlIjoiIiwiY2l0eSI6IiIsImNvdW50cnkiOiIiLCJwaG9uZU51bWJlciI6IiJ9fSwiam9pbnRCZXRzIjpbXSwiZ3JvdXBzIjpbeyJuYW1lIjoiVGVzdCIsIm1lbWJlcnMiOltdfV19

Base64 decoded: {"configuration":{"shop":{"name":"España","addressLine1":"","addressLine2":"","postalCode":"","city":"","country":"","phoneNumber":""}},"jointBets":[],"groups":[{"name":"Test","members":[]}]}

Answer 3

The old Base64 utility add linebreaks every 76 characters in Java8. The result looks like that:

/9j/4AAQSkZJRgABAgAAAQABAAD/2wBDAAgGBgcGBQgHBwcJCQgKDBQNDAsLDBkSEw8UHRofHh0a
HBwgJC4nICIsIxwcKDcpLDAxNDQ0Hyc5PTgyPC4zNDL/2wBDAQkJCQwLDBgNDRgyIRwhMjIyMjIy
MjIyMjIyMjIyMjIyMjIyMjIyMjIyMjIyMjIyMjIyMjIyMjIyMjIyMjIyMjL/wAARCABkAGQDASIA
AhEBAxEB/8QAHwAAAQUBAQEBAQEAAAAAAAAAAAECAwQFBgcICQoL/8QAtRAAAgEDAwIEAwUFBAQA
AAF9AQIDAAQRBRIhMUEGE1FhByJxFDKBkaEII0KxwRVS0fAkM2JyggkKFhcYGRolJicoKSo0NTY3
ODk6Q0RFRkdISUpTVFVWV1hZWmNkZWZnaGlqc3R1dnd4eXqDhIWGh4iJipKTlJWWl5iZmqKjpKWm
...

It seems that this behaviour changed with some version. At least with Java11 the decoder is not accepting line-breaks anymore. To avoid the problem you could change you method

public static String decryptString(String string) {
    byte[] valueDecoded = Base64.getDecoder().decode(string.replace("\n","").replace("\r","");
    return new String(valueDecoded);
}